1. Field of the Invention
The field of art to which the claimed invention pertains is the catalytic cracking of hydrocarbons. More specifically, the claimed invention relates to a process for the passivation of contaminating metals on a fluidized cracking catalyst.
2. Description of the Prior Art
There are a number of continuous cyclical processes employing fluidized solid techniques in which carbonaceous materials are deposited on the solids in the reaction zone and the solids are conveyed during the course of the cycle to another zone where carbon deposits are at least partially removed by combustion in an oxygen-containing medium. The solids from the latter zone are subsequently withdrawn and reintroduced in whole or in part to the reaction zone.
One of the more important processes of this nature is the fluid catalytic cracking process for the conversion of relatively high-boiling hydrocarbons to lighter hydrocarbons boiling in the heating oil and gasoline (or lighter) range. The hydrocarbon feed is contacted in one or more reaction zones with the particulate cracking catalyst maintained in a fluidized state under conditions suitable for the conversion of hydrocarbons.
A common problem in the fluid catalytic cracking process is the gradual deterioration of the catalyst due to the deposition on the catalyst of metal contaminants contained in the hydrocarbon feed, such as nickel, vanadium and iron. These deposited metal contaminants increase the production of hydrogen, light gases and coke at the expense of the highly desired gasoline.
The art teaches many techniques for dealing with these undesirable metal contaminants. Such techniques can be divided into two broad catagories, one being the passivation of the contaminants by reacting the catalyst with a passivating agent, which forms relatively innocuous complexes with the metal contaminants, and the other being the physical removal of the contaminants from the catalyst. Examples of techniques falling within the former category are as taught or claimed in U.S. Patent Publication Nos. 2,758,097 (reaction with phosphorous pentoxide); 3,711,422 (reaction with an antimony compound); and 4,025,458 (reaction with a chemical complex containing antimony). Examples of techniques falling within the latter category are as taught or claimed in U.S. Patent Publication Nos. 3,252,918; 3,324,044; 4,013,546; and 4,014,815.
There is also art that teaches reduction and sulfiding treatment of non-fluidized moving catalyst beds to temper the activity of certain desired metals, such as those contained in Group VIII of the Periodic Table, intentionally added to the catalyst. The processes in which these moving catalyst beds are used include processes such as hydrocracking and reforming. U.S. Pat. No. 3,838,038 is an example of such art teaching reduction and sulfiding of a non-fluidized catalyst containing certain desired metals.
We have found a process for passivating an undesired metal contaminant on a fluid cracking catalyst by reaction with a reducing gas.